The present invention relates to a fixed-amount-of-liquid ejecting method and apparatus, which are suitably used for ejecting a liquid in a fixed amount, the liquid including a viscous fluid and a material having consistency.
Japanese Unexamined Patent Publication No. 4-49108, for example, discloses one example of a conventional fixed-amount-of-liquid ejecting apparatus for use in regularly or irregularly coating an electronic material on a board in the form of points and lines in semiconductor manufacturing processes. In a disclosed screw type ejecting apparatus, the amount of a liquid ejected through an ejection port is controlled in accordance with such a parameter as the speed and cycle time of rotation of a screw, etc. With the disclosed apparatus, the rotational speed and the stop timing of the screw are controlled with high accuracy. Therefore, the amount of the ejected liquid is stabilized and the ejection of the liquid in a fixed amount can be achieved even in a continuous ejection mode without being affected by the viscosity and fluidity of the liquid and the amount of the liquid present in a reservoir.
In the above prior art apparatus, however, the liquid is ejected and stopped respectively upon rotation and stoppage of the screw, and the ejection port is left in a physically open state during the time in which the ejection is stopped. This has raised the following problem, particularly in the case of the liquid having a low viscosity or the case of pressurizing the liquid in the reservoir. If there is a relatively large clearance between an outer peripheral surface of the screw and an inner peripheral surface of a screw housing, the liquid is not positively shut off at the time of stopping the ejection of the liquid, and the liquid tends to leak due to the own weight and a force applied to pressurize the liquid. On the other hand, if the clearance between the outer peripheral surface of the screw and the inner peripheral surface of the screw housing is set to a small value to overcome the above problem, another problem has arisen in that fillers, for example, mixed in the electronic material are broken.
With the view of solving the above-described problems experienced in the prior art, an object of the present invention is to provide a method and apparatus for ejecting a liquid, by which an ejection port of an ejection valve is mechanically opened and closed, and hence which can more positively shut off the liquid at the time of stopping the ejection of the liquid and can securely avoid a leakage of the liquid without a risk of breaking fillers.
In the method of ejecting a liquid in a fixed amount according to the present invention, when ejecting the liquid in the fixed amount from a liquid reservoir through an ejection valve, a pressure of the liquid supplied from the liquid reservoir to the ejection valve is controlled depending on the liquid pressure near an ejection port of the ejection valve, and the ejection port is mechanically opened and closed.
With the method of the present invention, when ejecting the liquid in a relatively small fixed amount, the pressure in a flow passage after the end of the ejection, particularly the pressure near the ejection port, is controlled to be kept at a predetermined specific value, whereby the subsequent ejection of the liquid can be always performed under the constant flow passage condition. Accordingly, by properly setting the force, time, etc. for pressurizing the liquid in the liquid reservoir, the ejection of the liquid in an amount corresponding to the set values can be repeatedly reproduced with high reliability.
On the other hand, when ejecting the liquid in a relatively large fixed amount, in addition to the above control, the pressure of the supplied liquid is controlled also during the ejection of the liquid based on the detected result of the liquid pressure in such a manner, for example, that variations of the detected pressure is kept as small as possible. Consequently, the liquid can be ejected in the fixed amount as intended.
Further, by mechanically opening the ejection port of the ejection valve in timed relationship with an increase of the force pressurizing the liquid in the liquid reservoir, the ejection of the liquid can be started without a time lag. In addition, at the end of the ejection, by controlling the ejection valve so as to offset an increase of the pressurizing force and mechanically closing the ejection port of the ejection valve, one cycle of ejecting the liquid in the fixed amount can be ended with positive shutting-off of the liquid without a risk of liquid leakage.
After one cycle of ejecting the liquid in the fixed amount has been ended, the liquid pressure in the flow passage is controlled to be kept at the predetermined specific value depending on the liquid pressure near the ejection port of the ejection valve in a similar way as described above.
The apparatus for ejecting a liquid in a fixed amount from a liquid reservoir according to the present invention comprises a liquid reservoir, means for pressurizing the liquid in the liquid reservoir directly or indirectly, an ejection valve communicating with the liquid reservoir and having an ejection port mechanically opened and closed, a pressure sensor for detecting a pressure of the liquid near the ejection port, and control means for controlling operation of the pressurizing means in accordance with a signal from the pressure sensor.
With the apparatus of the present invention, using a pressure signal and a pressurizing time signal supplied to the pressurizing means, the liquid in the liquid reservoir is pressurized for a time corresponding to the pressurizing time signal so that the liquid is held under a pressure corresponding to the pressure signal. Further, the ejection valve is opened in timed relationship with the operation of the pressurizing means. As a result, the ejection of the liquid can be started without a time lag.
At the time when the time during which the liquid is pressurized by the pressurizing means reaches a predetermined time and the amount of the ejected liquid reaches a predetermined amount, the ejection valve is mechanically closed in timed relationship with the stop operation of the pressurizing means. The ejection port of the ejection valve is thereby physically closed. Therefore, the liquid is positively shut off and an accidental leakage of the liquid after that can be perfectly prevented.
After one cycle of ejecting the liquid in the fixed amount has been ended, the liquid pressure near the ejection port is detected by the pressure sensor, and a detected pressure signal at this time is inputted to the control means. In accordance with the input signal, the control means controls the pressurizing means to raise or lower the liquid pressure so that the residual liquid pressure near the ejection port becomes the predetermined specific value. It is a matter of course that if the detected liquid pressure coincides with the predetermined specific value, the pressurizing means is not required to be operated again.
By always keeping the liquid pressure near the ejection port and hence the pressure in the liquid flow passage at the constant values after the end of the ejection as described above, variations of the flow passage condition are eliminated. At the time of starting the next cycle of ejecting the liquid in the fixed amount, the force, time, etc. for pressurizing the liquid can be determined with no need of taking into account indefinite factors. In addition, the liquid can be ejected in the fixed amount with high accuracy.
When one cycle of liquid ejection is continued for a relatively long time as experienced, for example, when the liquid is coated in the linear form, it is preferable that the pressure detection by the pressure sensor is also performed during the ejection and the liquid pressurizing force applied from the pressurizing means is controlled in accordance with the detected result.
In the apparatus of the present invention, preferably, the ejection valve comprises a needle valve. Since the size of a needle can be made in itself sufficiently small, the needle can be smoothly and quickly displaced to open and close by a relatively small driving force even under a high pressure on the order of, for example, 100-200 kgf/cm2. It is therefore possible to shut off the liquid more positively at the end of the ejection, and to eliminate a time lag more effectively at the start of the ejection.
In addition, since the required driving force is relatively small, the overall size of the ejection valve can be reduced.
More preferably, the needle valve is provided with a liquid pressure compensating piston.
With the above feature, the apparatus can operate so as to compensate pressure variations in the liquid passage, particularly at and near the ejection port, more easily, quickly and accurately in combination with back and forth movement of the liquid pressure compensating piston. One example of the combined operation is as follows. When the needle valve is opened, the volume occupied by the needle in an area near the ejection port is reduced. Conversely, when the needle valve is closed, the volume occupied by the needle in the area near the ejection port is increased. In the former case, a decrease of the liquid pressure near the ejection port can be prevented by moving forth the liquid pressure compensating piston. In the latter case, an increase of the liquid pressure near the ejection port can be prevented by moving back the liquid pressure compensating piston.
Accordingly, the liquid pressure compensating piston can be employed in addition to or in place of the pressurizing means for the purpose of controlling the residual liquid pressure to the predetermined specific value after the end of the ejection.
Further, when an ejection nozzle requires to be moved relative to a workpiece in the apparatus of the present invention, the ejection nozzle is preferably mounted to a manipulator which is based on the Cartesian coordinate system and enables the ejection nozzle to be displaced in three dimensional directions. More preferably, the manipulator is controlled in synchronous relation to control of the pressurizing means and control of the ejection valve.
According to the present invention, as will be apparent from the above description, since the ejection port of the ejection valve is mechanically opened and closed, positive shutting-off of the liquid at the time of stopping the ejection of the liquid can be more securely achieved without breaking fillers which are sometimes mixed in the liquid, and a leakage of the liquid through the ejection port can be prevented sufficiently.
Additionally, by setting the bore diameter of an air cylinder, which serves as means for pressurizing the liquid, to be much larger than the inner diameter of the liquid reservoir, the liquid pressure can be raised up to a required level even when the line air pressure in a general factory is relatively low. As a result, efficiency of the liquid ejecting work can be improved as intended.